This invention pertains to shock protection of disk drives. More particularly the invention is directed to an apparatus and method of effectively locking a disk drive actuator in a parking position so that the actuator is immovable when subjected to relatively high shock loadings.
The present invention particularly finds utility in magnetic memory storage disk drives utilizing a voice coil motor-driven rotary actuator having read/write transducers accessing one or more disks, normally on both surfaces of the disk. Upon powering down of the actuator, the actuator and its attached read/write transducers is driven to a parking position or landing zone normally at the I.D. of the circular memory storage "tracks" on the disk. When the power is shut down, the actuator when subjected to jars, shocks or vibrations, may pivot damaging the tranducer heads and the magnetic surfaces on the adjacent disk(s). While the invention is described in terms of magnetic data storage disks, optical transducer(s) may also be incorporated in the actuator and the actuator appropriately parked and locked using the invention.
Various systems for moving a rotary actuator to a parking position and locking the actuator at that position have been employed. It is known (U.S. Pat. No. 4,679,102) to employ the back EMF of a disk-driving spindle motor as it spins down to drive a stepper motor so that the stepper motor moves the actuator to the parking position.
U.S. Pat. No. 4,654,735 describes latch elements including detents for holding the actuator and its transducer heads latched in an inoperative landing position against a stop. Triggering of the latch has been accomplished by use of a charged capacitor energizing the coil of a voice-coil motor or by a coil current (back EMF) generated by a spindle motor coasting to a half whenever the power thereto is purposely or inadvertently shut off. An over-center toggle spring has been employed with a spring force chosen so that the latching force is great enough not to be overcome by jolts or shocks of some force but small enough to be overcome by the forces in the voice coil motor when it is energized to move during normal head-positioning operation. The '735 patent also describes that the spring urges the latch to a latched position.
A magnet as seen in U.S. Pat. No. 4,594,627 has also been employed to magnetically attach a bobbin of a voice-coil linear motor to a limit stop with the linear motor upon start-up having sufficient power to overcome the magnetic attraction of the contacting magnet and stop. U.S. Pat. No. 4,751,595 describes the use of a solenoid to move a locking position lever into a locking upon the turning-off of a disk drive actuator.
Specifications for a disk drive using the present invention include a requirement that the drive withstand an operating shock loading of 10 G's and non-operating (latched position) shock load from dropping or jarring of 300 G's plus angular accelerations of from about 10,000 to 20,000 radians per second per second from dropping on a corner of the drive or computer. Miniaturization of disk drives have compounded the latch problem faced by design engineers. For example, the above specifications further recite an overall disk drive envelope size of 70 mm long, 50.0 mm wide and 12.5 mm thick which accommodates one 1.8 inch diameter disk [48 mm] providing up to 40 Mb of magnetic storage. The foot print of the disk drive actually is smaller than a business card.
With few exceptions the prior art constructions have used a so-called "passive" latch where two magnetic parts or other latch such as a solenoid-operated latch lever are brought into physical contact--magnet-to-pole piece or lever finger-to-detent.
FIG. 13 schematically illustrates the effect of having a high actuator torque required to disengage a prior art latch, e.g. a magnet-to-pole piece contacting or nearly contacting latch, on start-up of the drive. The latch torque L.sub.T is plotted against the angle .theta. motion of the rotary actuator. The distance LZ represents the landing zone or parking position of the actuator and the distance DZ represents the essentially radial data zone of the disk. The desired track of the actuator across the disk data storage tracks is shown by the closed loop A which is effected by normal bias forces due to friction in the actuator bearings, bias from the flexing of the flex circuit, and windage. If one employs a high latching torque H, the application of the approximate square law for the force decrease versus the distance between the latching elements would mean that the actuator heads would intersect the loop A approximately at point B resulting in lost disk space. Thus in prior art devices the designer in order to save the data storage area and minimize the landing zone LZ generally will accept the use of a low latching torque L so that the plot intersects loop A at point C.